# Antifungal Activity of Acorus calamus Essential Oil Against Rice Blast Fungus Magnaporthe oryzae and Its Composition Characterization

## TL;DR

This study shows that Acorus calamus essential oil strongly inhibits the rice blast fungus, making it a promising natural fungicide.

## Contribution

The study identifies Acorus calamus essential oil as a potent antifungal agent against Magnaporthe oryzae with detailed composition and mechanism analysis.

## Key findings

- Acorus calamus essential oil (ACEO) had the strongest antifungal effect with an EC50 of 0.37 μL/mL.
- ACEO disrupted fungal hyphal morphology and cellular integrity, reducing pathogenicity significantly.
- GC-MS analysis revealed β-asarone and isoshyobunone as the major active components of ACEO.

## Abstract

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases affecting global rice production. Plant essential oils (EOs) have been considered as a promising green alternative to synthetic fungicides. In this study, the antifungal activities of five plant EOs—Acorus calamus, Citrus reticulata, Syzygium aromaticum, Paeonia suffruticosa, and Melaleuca viridiflora—against M. oryzae were evaluated using the mycelial growth rate method. Among them, A. calamus EO (ACEO) exhibited the most pronounced inhibitory effect, with an EC50 value of 0.37 μL/mL. It significantly delayed or inhibited conidial germination and appressorium formation. At higher concentrations (≥1 μL/mL), it also caused morphological abnormalities in appressoria. Observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the EO treatment caused hyphal surface wrinkling, cell wall thinning, organelle dissolution, and vacuolation. Pathogenicity tests further confirmed that ACEO reduced the virulence of the fungus remarkably, with nearly complete loss of pathogenicity at a concentration of 1 μL/mL. Finally, ACEO was analyzed using gas chromatography-mass spectrometry (GC-MS). The most abundant constituents identified were β-asarone (19.83%) and isoshyobunone (14.92%). Together, these findings demonstrate that ACEO impairs fungal pathogenicity by disrupting hyphal morphology and cellular integrity, highlighting its potential as an effective and eco-friendly fungicide for controlling rice blast.